1. Field of the Invention
The present invention relates to a switch used, for example, to control the lighting of a lamp. It more specifically relates to a switch for vehicles used, for example, to control the lighting of a stop lamp when a car brake pedal is operated, and to a method for manufacturing the switch.
2. Background Art
In recent years, push switches for vehicles have been used more and more to control the lighting of a stop lamp in response to the operation of a brake pedal. A push switch for vehicles turns on the stop lamp when the brake pedal is pressed, and turns off when the driver's foot leaves the brake pedal.
One conventional switch for vehicles, which is disclosed in Japanese Patent Unexamined Publication No. 2001-297654, will be described as follows with reference to FIGS. 7 and 8.
As shown in FIG. 7, the conventional push switch for vehicles is provided with box-like case 1 which is made of insulating resin and whose top surface has an opening, and operating body 2 made of insulating resin. Case 1 is provided with a plurality of downwardly projecting fixed contacts 3 in the vicinity of the opening, and with terminals 3A extending downward from bottom surface 1A of case 1.
Between movable contacts 4 made of a conductive metal and the bottom surface of case 1 is held push spring 5 in a slightly compressed condition. Push spring 5 pushes movable contacts 4 upward to bring movable contacts 4 into contact with fixed contacts 3. Fixed contacts 3 are electrically connected with each other via movable contacts 4 so as to form switch contacts.
The conventional push switch for vehicles is further provided with coiled return spring 6, and cover 7 for covering the opening of the top surface of case 1. Return spring 6 is held in a slightly compressed condition between the bottom surface of operating body 2 and bottom surface 1A of case 1, thereby energizing operating body 2 upward.
Cover 7 has hollow cylindrical part 7A which extends upward and which accommodates operating shaft 2A of operating body 2 in such a manner as to be vertically movable. The top end of operating shaft 2A extends beyond hollow cylindrical part 7A.
The push switch for vehicles thus structured is generally installed in front of a car brake pedal in such a manner that operating shaft 2A of operating body 2 is pressed by an arm or the like. Terminals 3A of fixed contacts 3 are connected to the stop lamp via a connector or the like.
When the brake pedal is not pressed, operating shaft 2A of operating body 2 is pushed downward. More specifically, push spring 5 and return spring 6 are compressed, so that movable contacts 4 are lowered to be away from fixed contacts 3, and that fixed contacts 3 are electrically disconnected from each other. As a result, the stop lamp is turned off.
In this condition, when the brake pedal is pressed, the arm is separated from operating shaft 2A to remove the pressing force applied on operating shaft 2A. Consequently, the elastic restoring force of return spring 6 moves operating body 2 upward, and movable contacts 4 are pushed up by push spring 5 so as to come into resilient contact with fixed contacts 3. As a result, fixed contacts 3 are electrically connected with each other, thereby turning on the stop lamp.
As such stop lamps whose lighting is controlled by a switch for vehicle, electric lamps, LEDs (Light Emitting Diodes) and the like are generally used. In the case of using an electric lamp, a comparatively large current of about 10 A is applied at 12Vdc, whereas in the case of using an LED, as small as about 0.5 A to 1 A is applied at 12Vdc.
As shown in the partial cross sectional view shown in FIG. 8, in the case where the surface of each movable contact 4 and the surface of each fixed contact 3 are smooth and are in contact with each other at a single point and where an LED or the like requiring a small current is used as the stop lamp, an oxide film or the like forms on the surfaces of fixed contacts 3 and/or on the surfaces of movable contacts 4, thereby making the contact unstable.
To overcome this inconvenience, Japanese Utility Model Unexamined Publication No.S63-186020 discloses a contact device in which the surface of at least one of fixed contact 11 and movable contact 12 is designed to have a surface roughness of 0.5 to 10 μm. The aim of this is to stabilize the contact by roughening the surface so as to create a plurality of contact points. However, the disclosed method for surface roughening, that is, press working by using a press jig having the predetermined surface roughness can only provide the contact surface or surfaces with projections whose tips are smooth or flat. This has little effect on breaking an oxide film or the like formed on the contact surface or surfaces, thereby making it difficult to stabilize the contact with a small electric current.
Furthermore, when the surface roughness of the contact surface or surfaces is 0.5 to 10 μm, if an insulating oxide enters from outside the switch or develops due to the repeated opening and closing of the contacts, the entered insulating oxide or developed oxide with the size of 10 μm or larger can be projected from the contact surface or surfaces so as to cause the contacts to come into contact with each other via the projected insulating oxide, thereby making it difficult to achieve stable contact.